Born in Birmingham, Devlin began to play competitive football for Boldmere St. Michaels Reserves in the early 1980s. He joined Stafford Rangers in 1991, following his release by Tamworth, in just one season playing for the club Devlin was spotted by a number of Football League scouts.

Although Devlin had limited chances in his first season the club suffered the pain of relegation from the Football League First Division by finishing 21st. With the Premier League been formed the following season the club were effectively relegated to the same league although they were now in the second tier of English football.

The following season did not look much better for Notts County and Devlin as the club were again involved in a relegation battle, manager Neil Warnock left the club and Mike Walker came in and put a stop to the club's drop by steering the club to a 17th place finish.

The following season Devlin began to show his form and his performances shot the club to a 7th place finish and missed out on the play-offs by one position.

Devlin, however stayed loyal to the club and began the 1995/96 season in the Football League Second Division and some of the impressive displays that Devlin had showed previously returned and sent Notts County to the top end of the table and an instant return to the First Division looked on the cards, but Devlin was a wanted man and in January 1996 his form was enough to attract the attention of Birmingham City, who signed him for a fee of £250,000.

During his time with Notts County Devlin made a total of 141 appearances and scored 25 goals.

Devlin's Birmingham City career got off to a great start and the player showed he was still more than capable of playing in the First Division by scoring a further seven times for the club before the end of the 1995/96 season.

The following season Devlin scored 16 times, and he contributed a further five goals. In total Devlin played 76 games scoring 28 goals.

Devlin joined Sheffield United in February 1998, signed by Steve Thompson for £200,000. After a string of substitute appearances he made his full debut on 13 April in a 1–1 draw away at Swindon Town. He scored his first goal for the Blades in another away draw later that month, this time finishing 3–3 at Tranmere Rovers.

Devlin showed himself to be a hard-working player, but with a habit of getting booked, picking up 11 yellow cards in his first season with the club. He notched 24 goals in his 145 games for the club. November 1998 briefly saw him loaned back to Notts County where he played a further five times.

In February 2002, Devlin was to return to Birmingham, manager Steve Bruce signing him to provide cover for his main strikers. This second spell, including promotion to the Premier League, saw Devlin play 77 times, scoring seven goals, however at the end of the 2003/04 season he was released.

Soon after Devlin joined Ray Lewington and Watford. He added steel and experience to the Championship side. During his first season, the 2003/04 season he made 39 appearances and scored 3 goals, the club finished in 16th position in the table.

The 2004/05 was an eventful one for Watford and Devlin in his second season with the club, again Devlin was a regular with the club, but after February he did not play for the club again that season due to injury. Lewington found himself on his way out in March, much to the anger of many Watford fans, who believed that the dismissal was harsh and that he had done his best with resources available to him, even so Watford hired Leeds United coach Aidy Boothroyd for his first taste as a manager. Boothroyd masterminded the club to safety when relegation had looked a certainty. During the season Devlin made 17 appearances and scored just once, with Watford finishing 18th and avoiding relegation.

The 2005/06 was Devlins chance to try and impress new manager Boothroyd, who had failed to see him play the previous season with the injury coming when it did. It turned out to be Devlin's last season as a Watford player, he returned to the squad at the start of the season, and played as a regular for the season and made 23 appearances and scored two goals, before Boothroyd allowed him to leave on a free transfer to Walsall on 17 January 2006.

Devlin's Walsall career took the worst possible start when he was injured on his debut just a week later. Upon his return to the first team he was sent off for an elbow to the face of an opponent in a 2–2 draw with Scunthorpe United. After just eight appearances and a goal against Swansea City[2] for Walsall, Devlin asked to be released after being left on the bench by then manager Kevan Broadhurst for a game against A.F.C. Bournemouth in April 2006. It was a controversial move, coming as it did whilst Walsall were in the midst of a struggle to remain in League One, in which they ultimately failed.

On 7 September 2006, Devlin returned to his roots by joining his youth team club, Tamworth. This bridged a 16-year gap away from the club. However on 4 October, and just four appearances under his belt, it was announced that Devlin had left the club by mutual consent, as he was unable to commit the necessary time.

He then had a brief stint with Sutton Coldfield Town before signing for Halesowen Town on 19 February 2007, where he played in midfield. He joined Rugby Town as player/assistant manager in January 2008,[3] but left for personal reasons after little more than a week in the post.[4]

Devlin rejoined Sutton Coldfield Town at the end of March 2008[5] – the fourth time he had returned to a former club, the previous three being Notts County, Birmingham City and Tamworth – but left at the start of the 2008–09 season citing a "breakdown in communication" with the manager.[6]

Devlin won the first of his 10 Scotland caps in a friendly against Canada in October 2002, and last played for them in September 2003, against the Faroe Islands in a Euro 2004 qualifying match. Devlin qualified to play for Scotland via his father being from Coatbridge.[9]

Devlin said of his home debut against Republic of Ireland at Hampden Park, "Playing at Hampden has always been a dream of mine and to finally achieve that made the match the proudest night of my career. I had 30-odd people in the stand watching me and it cost me an absolute fortune to make sure they could all be here. There were 23 of the clan from up here and a further seven flew up from down south."[10]